jerry-sl

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

jerry-sl

# Set variables in .bashrc file

# don't forget to change your path correctly!

export GOPATH=$HOME/golang
export GOROOT=/usr/local/opt/go/libexec
export PATH=$PATH:$GOPATH/bin
export PATH=$PATH:$GOROOT/bin

jerry-sl

go get -u golang.org/x/crypto/bcrypt
go get -u golang.org/x/crypto/blowfish
go get -u golang.org/x/crypto/bn256
go get -u golang.org/x/crypto/cast5
go get -u golang.org/x/crypto/curve25519
go get -u golang.org/x/crypto/hkdf
go get -u golang.org/x/crypto/md4
go get -u golang.org/x/crypto/nacl/box
go get -u golang.org/x/crypto/nacl/secretbox
go get -u golang.org/x/crypto/ocsp

jerry-sl

Not all random values are created equal - for security-related code, you need a specific kind of random value.

A summary of this article, if you don't want to read the entire thing:

• Don't use Math.random(). There are extremely few cases where Math.random() is the right answer. Don't use it, unless you've read this entire article, and determined that it's necessary for your case.
• Don't use crypto.getRandomBytes directly. While it's a CSPRNG, it's easy to bias the result when 'transforming' it, such that the output becomes more predictable.
• If you want to generate random tokens or API keys: Use uuid, specifically the uuid.v4() method. Avoid node-uuid - it's not the same package, and doesn't produce reliably secure random values.
• If you want to generate random numbers in a range: Use random-number-csprng.

You should seriously consider reading the entire article, though - it's

jerry-sl

@interface ApplicationDelegate<UIApplicationDelegate>
@end

@implementation ApplicationDelegate
- (RACSignal *)rac_registeredForRemoteNotifications {
    RACSignal *signal = objc_getAssociatedObject(self, _cmd);
    if (signal != nil) return signal;
    
    RACSignal *didRegisterForRemoteNotification = [[self rac_signalForSelector: @selector(application:didRegisterForRemoteNotificationsWithDeviceToken:) fromProtocol: @protocol(UIApplicationDelegate)] map: ^(RACTuple *tuple) {
        return tuple.second;

jerry-sl

typedef enum {
    AGCommandPriorityLow = -10,
    AGCommandPriorityDefault = 0,
    AGCommandPriorityHigh = 10
} AGCommandPriority;

@interface AGCommand : NSObject

@property(nonatomic, weak) NSObject *firingObject;
@property(nonatomic, readonly) SEL action;

jerry-sl

typedef enum {
    AGCommandPriorityLow = -10,
    AGCommandPriorityDefault = 0,
    AGCommandPriorityHigh = 10
} AGCommandPriority;

@interface AGCommand : NSObject

@property(nonatomic, weak) NSObject *firingObject;
@property(nonatomic, readonly) SEL action;

jerry-sl

#import <UIKit/UIKit.h>

@interface DateFlowLayout : UICollectionViewFlowLayout

@end